Methods and apparatuses for improving quality of positioning

ABSTRACT

Methods and apparatuses of improving quality of positioning are disclosed. According to aspects of the present disclosure, a transition from a short training field to a long training field in one or more communication messages between two wireless stations may be detected. A station may then determine a first arrival correction time based on the transition from the short training field and the long training field. With the first arrival correction time, more accurate timing of communications between the two wireless stations may be determined and used for improving quality of positioning applications.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No.61/875,558, “Methods and Apparatuses for Improving Quality ofPositioning,” filed Sep. 9, 2013, and U.S. provisional application No.61/877,881, “Methods and Apparatuses for Improving Quality ofPositioning,” filed Sep. 13, 2013, both assigned to the assignee hereof.The aforementioned United States applications are hereby incorporated byreference in their entirety.

FIELD

The present disclosure relates to the field of wireless communications.In particular, the present disclosure relates to methods and apparatusesfor improving quality of positioning.

BACKGROUND

In conventional positioning systems, using measurements of round-triptime (RTT) between two wireless terminals for positioning may produceinaccurate results. One of the reasons is that the guard interval inorthogonal frequency division multiplexing (OFDM) packets may typicallyintroduce hundreds of nanoseconds of uncertainty into the measurements,which may in turn introduce hundreds of meters of inaccuracy inpositioning.

SUMMARY

Methods and apparatuses for improving quality of positioning aredisclosed. According to aspects of the present disclosure, a transitionfrom a short training field to a long training field in a communicationmessage between two stations may be detected. A station may thendetermine a first arrival correction time based on the transition fromthe short training field and the long training field. With the firstarrival correction time, more accurate timing of communications betweenthe two stations may be determined and used for improving quality ofpositioning applications.

In one embodiment, one or more processors or digital signal processorsor combination thereof may be configured to receive a message at a firststation, where the message comprises at least a short training field anda long training field received from a second station, detect atransition from the short training field to the long training field,determine a first arrival correction time based at least in part on thetransition from the short training field to the long training field, andassist the second station to determine a range of the second station inaccordance with the first arrival correction time.

To detect the transition from the short training field to the longtraining field, the one or more processors may be configured to monitora window of impulse responses of the message received, generate anormalized energy level of the window of impulse responses with respectto time using the message received, and identify the transition from theshort training field to the long training field based at least in parton the normalized energy level exceeds a predetermined threshold. Thepredetermined threshold may represent a fraction of the normalizedenergy level of the window of impulse responses. In otherimplementations, a change of the slope of the normalized energy level ofthe impulse responses may be used to identify a transition from theshort training field to the long training field. For example, if thechange of the slope of the normalized energy level of the impulseresponses exceeds a predetermined threshold, a transition from the shorttraining field to the long training field may be identified.

To determine the first arrival correction time, the one or moreprocessors may be configured to determine a first arrival time using thetransition from the short training field to the long training field, anddetermine the first arrival correction time according to a differencebetween the first arrival time and an expected arrival time.

To assist the second station to determine the range of the secondstation in accordance with the first arrival correction time, the one ormore processors may be configured to transmit a first message to thesecond station, where the first message is used to compute an adjustedtime of reception of the first message from the first station using thefirst arrival correction time and to determine the range of the secondstation based at least in part on the adjusted time of reception of thefirst message. The one or more processors may be configured to transmita second message to the second station, where the second messageincludes an adjusted time stamp from the first station, and where theadjusted time stamp from the first station is used to determine therange of the second station.

Note that the adjusted time stamp from the first station may include atime of reception of acknowledgement from the second station plus thefirst arrival correction time. The adjusted time stamp from the firststation may also include a time of reception of acknowledgement from thesecond station plus the first arrival correction time and a randomnoise.

In another embodiment, a computer program product may include anon-transitory medium that stores instructions for execution by one ormore computer systems. The instructions may include instructions forreceiving a message at a first station, where the message comprises atleast a short training field and a long training field received from asecond station, instructions for detecting a transition from the shorttraining field to the long training field, instructions for determininga first arrival correction time based at least in part on the transitionfrom the short training field to the long training field, andinstructions for assisting the second station to determine a range ofthe second station in accordance with the first arrival correction time.

In yet another embodiment, a device may include a transceiver configuredto receive a message at the device, where the message comprises at leasta short training field and a long training field received from a secondstation, a control module including control logic and one or moreprocessors. The one or more processors or digital signal processors orcombination thereof may further include logic configured to detect atransition from the short training field to the long training field,determine a first arrival correction time based at least in part on thetransition from the short training field to the long training field, andassist the second station to determine a range of the second station inaccordance with the first arrival correction time.

In yet another embodiment, an apparatus may include means for receivinga message at the apparatus, where the message comprises at least a shorttraining field and a long training field received from a second station,means for detecting a transition from the short training field to thelong training field, means for determining a first arrival correctiontime based at least in part on the transition from the short trainingfield to the long training field, and means for assisting the secondstation to determine a range of the second station in accordance withthe first arrival correction time.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned features and advantages of the disclosure, as well asadditional features and advantages thereof, will be more clearlyunderstandable after reading detailed descriptions of embodiments of thedisclosure in conjunction with the non-limiting and non-exhaustiveaspects of following drawings. Like numbers are used throughout thefigures.

FIG. 1 illustrates an exemplary system environment according to aspectsof the present disclosure.

FIG. 2 illustrates exemplary messages flow between wireless stations(STAs) according to aspects of the present disclosure.

FIG. 3A illustrates an exemplary message according to aspects of thepresent disclosure.

FIG. 3B illustrates another exemplary message according to aspects ofthe present disclosure.

FIG. 3C illustrates yet another exemplary message according to aspectsof the present disclosure.

FIG. 4A illustrates an exemplary implementation for measuring firstarrival correction time according to aspects of the present disclosure.

FIG. 4B illustrates another exemplary implementation for measuring firstarrival correction time according to aspects of the present disclosure.

FIG. 5A illustrates an exemplary flow chart for implementing methods ofimproving quality of positioning according to aspects of the presentdisclosure.

FIG. 5B illustrates an exemplary implementation for detecting atransition from a short training field to a long training field of FIG.5A according to aspects of the present disclosure.

FIG. 5C illustrates an exemplary implementation for determining a firstarrival correction time of FIG. 5A according to aspects of the presentdisclosure.

FIG. 5D illustrates an exemplary implementation for assisting the secondstation to determine a position of FIG. 5A according to aspects of thepresent disclosure.

FIG. 6A illustrates another exemplary flow chart for implementingmethods of improving quality of positioning according to aspects of thepresent disclosure.

FIG. 6B illustrates an exemplary implementation for detecting atransition from a short training field to a long training field of FIG.6A according to aspects of the present disclosure.

FIG. 6C illustrates an exemplary implementation for determining a firstarrival correction time of FIG. 6A according to aspects of the presentdisclosure.

FIG. 6D illustrates an exemplary implementation for determining a rangeof the second station of FIG. 6A according to aspects of the presentdisclosure.

FIG. 7 illustrates an exemplary block diagram of a device according toaspects of the present disclosure.

FIG. 8 illustrates an exemplary block diagram of a computing platformaccording to aspects of the present disclosure.

DESCRIPTION OF EMBODIMENTS

Embodiments of improving quality of positioning are disclosed. Thefollowing descriptions are presented to enable any person skilled in theart to make and use the disclosure. Descriptions of specific embodimentsand applications are provided only as examples. Various modificationsand combinations of the examples described herein will be readilyapparent to those skilled in the art, and the general principles definedherein may be applied to other examples and applications withoutdeparting from the scope of the disclosure. Thus, the present disclosureis not intended to be limited to the examples described and shown, butis to be accorded the widest scope consistent with the principles andfeatures disclosed herein. The word “exemplary” or “example” is usedherein to mean “serving as an example, instance, or illustration.” Anyaspect or embodiment described herein as “exemplary” or as an “example”in not necessarily to be construed as preferred or advantageous overother aspects or embodiments.

As discussed below, particular message flows may enable effective andefficient measurements of a round trip time (RTT) in connection with atransmission of messages between wireless stations (STAs). In aparticular example, a STA may comprise any one of several types oftransceiver devices such as, for example, a mobile user station (e.g.,smartphone, notebook computer, tablet computer, etc.) or wirelessservice access device (e.g., wireless local area network (WLAN) accesspoint or femto cell). Particular message flows and fields in messagesframes may enable obtaining RTT measurements in sufficient accuracy formeasuring a range between the wireless STAs using fewer messages, forexample. Such a measured range may be used in any one of severalapplications including positioning operations, for example.

FIG. 1 illustrates an exemplary system environment according to aspectsof the present disclosure. As shown in FIG. 1, a mobile device 100 mayreceive or acquire satellite positioning system (SPS) signals 102 fromSPS satellites 104. In some embodiments, SPS satellites 104 may be fromone global navigation satellite system (GNSS), such as the GPS orGalileo satellite systems. In other embodiments, the SPS Satellites maybe from multiple GNSS such as, but not limited to, GPS, Galileo,Glonass, or Beidou (Compass) satellite systems. In other embodiments,SPS satellites may be from any one several regional navigation satellitesystems (RNSS) such as, for example, Wide Area Augmentation System(WAAS), European Geostationary Navigation Overlay Service (EGNOS),Quasi-Zenith Satellite System (QZSS), etc.

In addition, mobile device 100 may transmit radio signals to, andreceive radio signals from, a wireless communication network. In oneexample, mobile device 100 may communicate with a cellular communicationnetwork by transmitting wireless signals to, or receiving wirelesssignals from, base station transceiver 110 over wireless communicationlink 106. Similarly, mobile device 100 may transmit wireless signals to,or receive wireless signals from local transceiver 108 over wirelesscommunication link 112.

In a particular implementation, local transceiver 108 may be configuredto communicate with mobile device 100 at a shorter range over wirelesscommunication link 112 than at a range enabled by base stationtransceiver 110 over wireless communication link 106. For example, localtransceiver 108 may be positioned in an indoor environment. Localtransceiver 108 may provide access to a wireless local area network(WLAN, e.g., IEEE Std. 802.11 network) or wireless personal area network(WPAN, e.g., Bluetooth® network). In another example implementation,local transceiver 108 may comprise a femto cell transceiver capable offacilitating communication on wireless communication link 112 accordingto a cellular communication protocol.

In a particular implementation, base station transceiver 110 and localtransceiver 108 may communicate with one or more servers 140, 150 and/or160 over a network 130 through links 132. Here, network 130 may compriseany combination of wired or wireless communication networks. In aparticular implementation, network 130 may comprise Internet Protocol(IP) infrastructure capable of facilitating communication between mobiledevice 100 and servers 140, 150 or 160 through local transceiver 108 orbase station transceiver 110. In another implementation, network 130 maycomprise cellular communication network infrastructure such as, forexample, a base station controller or master switching center (notshown) to facilitate mobile cellular communication with mobile device100.

In particular implementations, and as discussed below, mobile device 100may have circuitry and processing resources capable of computing aposition fix or estimated location of mobile device 100. For example,mobile device 100 may compute a position fix based, at least in part, onpseudorange measurements to four or more SPS satellites 104. Here,mobile device 100 may compute such pseudorange measurements based, atleast in part, on pseudo-noise code phase detections in signals 102acquired from four or more SPS satellites 104. In particularimplementations, mobile device 100 may receive from server 140, 150 or160 positioning assistance data to aid in the acquisition of signals 102transmitted by SPS satellites 104 including, for example, almanac,ephemeris data, Doppler search windows, etc.

In other implementations, mobile device 100 may obtain a position fix byprocessing signals received from terrestrial transmitters fixed at knownlocations (e.g., such as base station transceiver 110) using any one ofseveral techniques such as, for example, advanced forward trilateration(AFLT) and/or observed time difference of arrival (OTDOA). In theseparticular techniques, a range from mobile device 100 may be measured tothree or more of such terrestrial transmitters fixed at known locationsbased, at least in part, on pilot signals transmitted by thetransmitters fixed at known locations and received at mobile device 100.Here, servers 140, 150 or 160 may be capable of providing positioningassistance data to mobile device 100 including, for example, locationsand identities of terrestrial transmitters to facilitate positioningtechniques such as AFLT and OTDOA. For example, servers 140, 150 or 160may include a base station almanac (BSA) which indicates locations andidentities of cellular base stations in a particular region or regions.

In particular environments such as indoor environments or urban canyons,mobile device 100 may not be capable of acquiring signals 102 from asufficient number of SPS satellites 104 or perform AFLT or OTDOA tocompute a position fix. Alternatively, mobile device 100 may be capableof computing a position fix based, at least in part, on signals acquiredfrom local transmitters (e.g., WLAN access points positioned at knownlocations). For example, mobile devices may obtain a position fix bymeasuring ranges to three or more indoor terrestrial wireless accesspoints which are positioned at known locations. Such ranges may bemeasured, for example, by obtaining a MAC ID address from signalsreceived from such access points and obtaining range measurements to theaccess points by measuring one or more characteristics of signalsreceived from such access points such as, for example, received signalstrength (RSSI) or round trip time (RTT). In alternativeimplementations, mobile device 100 may obtain an indoor position fix byapplying characteristics of acquired signals to a radio heatmapindicating expected RSSI and/or RTT signatures at particular locationsin an indoor area. In particular implementations, a radio heatmap mayassociate identities of local transmitters (e.g., a MAC address which isdiscernible from a signal acquired from a local transmitter); expectedRSSI from signals transmitted by the identified local transmitters, anexpected RTT from the identified transmitters, and possibly standarddeviations from these expected RSSI or RTT.

In particular implementations, mobile device 100 may receive positioningassistance data for indoor positioning operations from servers 140, 150or 160. For example, such positioning assistance data may includelocations and identities of transmitters positioned at known locationsto enable measuring ranges to these transmitters based, at least inpart, on a measured RSSI and/or RTT, for example. Other positioningassistance data to aid indoor positioning operations may include radioheatmaps, magnetic heatmaps, locations and identities of transmitters,route-ability graphs, etc. Other assistance data received by the mobiledevice may include, for example, local maps of indoor areas for displayor to aid in navigation. Such a map may be provided to mobile device 100as mobile device 100 enters a particular indoor area. Such a map mayshow indoor features such as doors, hallways, entry ways, walls, etc.,points of interest such as bathrooms, pay phones, room names, stores,etc. By obtaining and displaying such a map, a mobile device may overlaya current location of the mobile device (and user) over the displayedmap to provide the user with additional context.

In one implementation, a route-ability graph and/or digital map mayassist mobile device 100 in defining feasible areas for navigationwithin an indoor area and subject to physical obstructions (e.g., walls)and passage ways (e.g., doorways in walls). Here, by defining feasibleareas for navigation, mobile device 100 may apply constraints to aid inthe application of filtering measurements for estimating locationsand/or motion trajectories according to a motion model (e.g., accordingto a particle filter and/or Kalman filter). In addition to measurementsobtained from the acquisition of signals from local transmitters,according to a particular embodiment, mobile device 100 may furtherapply a motion model to measurements or inferences obtained frominertial sensors (e.g., accelerometers, gyroscopes, magnetometers, etc.)and/or environment sensors (e.g., temperature sensors, microphones,barometric pressure sensors, ambient light sensors, camera imager, etc.)in estimating a location or motion state of mobile device 100.

According to an embodiment, mobile device 100 may access indoornavigation assistance data through servers 140, 150 or 160 by, forexample, requesting the indoor assistance data through selection of auniversal resource locator (URL). In particular implementations, servers140, 150 or 160 may be capable of providing indoor navigation assistancedata to cover many different indoor areas including, for example, floorsof buildings, wings of hospitals, terminals at an airport, portions of auniversity campus, areas of a large shopping mall, etc. Also, memoryresources at mobile device 100 and data transmission resources may makereceipt of indoor navigation assistance data for areas served by servers140, 150 or 160 impractical or infeasible; a request for indoornavigation assistance data from mobile device 100 may indicate a roughor coarse estimate of a location of mobile device 100. Mobile device 100may then be provided indoor navigation assistance data covering areasincluding and/or proximate to the rough or coarse estimate of thelocation of mobile device 100.

In a particular implementation, particular messages flows betweenwireless STAs may be implemented for obtaining a measurement of RTTbetween the STAs for use in positioning operations as discussed above.In particular implementations, as described below, any STA may comprisea mobile device (e.g., mobile device 100) or a stationary transceiver(such as access point, stationary Bluetooth® device, local transceiver108, etc.). As such, an exchange of messages between wireless STAs maycomprise an exchange of messages between a mobile device and astationary transceiver, between two peer mobile devices, or between twostationary transceivers, for example.

FIG. 2 illustrates exemplary messages flow between wireless stations(STAs) according to aspects of the present disclosure. In this example,messages flow between wireless stations STAs including a sending station202 and a receiving station 204 are shown. In this context, the sendingSTA 202 or the receiving STA 204 may comprise any one of severaltransceiver devices including a mobile device (e.g., mobile device 100)or stationary access transceiver device (e.g., local transceiver 108),or stationary base station (e.g., 110). A receiving STA may obtain orcompute one or more measurements of RTT based, at least in part, ontiming of messages or frames transmitted between the receiving STA and asending STA. In one exemplary embodiment, sending STA 202 may be mobiledevice 100 and receiving STA 204 may be local transceiver 108 of FIG. 1.In another exemplary embodiment, sending STA 202 may be mobile device100 and receiving STA 204 may be stationary base station 110 of FIG. 1.In yet another exemplary embodiment, sending STA 202 may be anothermobile device (not shown) and receiving STA 204 may be mobile device 100of FIG. 1.

According to aspects of the present disclosure, the receiving STA maytransmit a timing measurement request message or frame (“Request”) tothe sending STA and receive an acknowledgement message or frame(“Acknowledgement”) transmitted in response. According to aspects of thepresent disclosure, the request message may include at least a shorttraining field, a long training field, and a transition from the shorttraining field to the long training field. Similarly, theacknowledgement message may also include at least a short trainingfield, a long training field, and a transition from the short trainingfield to the long training field. The receiving STA may then obtain orcompute an RTT measurement based, at least in part, on time stamp values(t1, t4) provided in timing measurement messages or frames (“M”)received from the sending STA. In one example implementation, areceiving STA may compute an RTT measurement as (t4−t1)−(t3−t2), wheret2 and t3 are the time of receipt of a previous timing measurementmessage or frame and transmission of preceding acknowledgement messageor frame, respectively. The receiving STA may transmit a series oftiming measurement request messages in a burst to obtain a correspondingnumber of RTT measurements which may be combined for removal ofmeasurement noise in computing a range between the receiving and sendingSTAs.

FIG. 3A illustrates an exemplary message according to aspects of thepresent disclosure. The message includes packets L-SFT 302, L-LTF 304,L-SIG 306 and data 308. L-STF 302 represents short training field for alegacy or non-high-throughput (non-HT) device. L-LTF 304 represents longtraining field for a legacy or non-HT device. L-SIG 306 representssignal field for a legacy or non-HT device. Exemplary time durations ofL-SFT 302, L-LTF 304, and L-SIG 306 may be approximately 8 microseconds(us), 8 us, and 4 us, respectively. In other implementations, L-SFT 302,L-LTF 304, L-SIG 306 may have different time durations. In this example,the transition between a short training field and a long training fieldwould occur between the packets 302 and 304.

FIG. 3B illustrates another exemplary message according to aspects ofthe present disclosure. In the example shown in FIG. 3B, the messageincludes packets for both legacy devices as well as for high-throughput(HT) devices. Similar to the example of FIG. 3A, the message includespackets L-SFT 312, L-LTF 314, L-SIG 366. In addition, the messageincludes packets HT-SIG 318, HT-STF 320, HT-LTF 322 a, HT-LTF 322 b, anddata 324. HT-STF 320 represents short training field for a HT devicehaving duration of approximately 4 microseconds. HT-LTF 322 a or 322 brepresents long training field for a HT device having duration ofapproximately 4 microseconds. HT-SIG 318 represents signal field for aHT device having duration of approximately 4 microseconds. Exemplarytime durations of HT-STF 320, HT-LTF 322 a, HT-LTF 322 b and HT-SIG 318may be approximately 4 microseconds. In other implementations, HT-STF320, HT-LTF 322 a, HT-LTF 322 b and HT-SIG 318 may have different timedurations. In this example, the transition between L-STF and L-LTF wouldoccur between the packets 312 and 314; and the transition between HT-STFand HT-LTF would occur between the packets 320 and 322 a.

FIG. 3C illustrates yet another exemplary message according to aspectsof the present disclosure. In this example, the message includes packetsfor high throughput devices. Similar to the example shown in FIG. 3B,the message includes packets HT-STF 332, HT-LTF 334, HT-SIG 336, HT-SIG338, HT-STF 340, HT-LTF 342 a, HT-LTF 342 b, and data 344. In thisexample, the transition between HT-STF and HT-LTF would occur betweenthe packets 332 and 334, as well as between packets 340 and 342 a.

FIG. 4A illustrates an exemplary implementation for measuring firstarrival correction time according to aspects of the present disclosure.As shown in FIG. 4A, the horizontal axis represents time (shown as “n”)and the vertical axis represent a normalized energy level (shown as“|h(n)|²”) of a window of impulse response of a message received betweenthe sending station 202 and the receiving station 204 of FIG. 2.Referring to FIG. 2, the message can be, but not limited to: 1) therequest sent from station 204 to station 202; 2) the acknowledgementsend from station 202 to station 204; 3) the message sent from station202 to station 204 at time t1, which may be received at station 204 attime t2; 4) the ACK sent from station 204 to station 202 at time t3which may be received at station 202 at time t4; 5) the message thatincludes t1 and t4 sent from station 202 to station 204; or 6) otheracknowledgements or messages sent between the two stations.

According to aspects of the present disclosure, a station may beconfigured to monitor a window of impulse responses of the messagereceived. Then, the station may be configured to generate a normalizedenergy level of the window of impulse responses with respect to timeusing the message received, which may be represented by graph 402 asshown in FIG. 4A. The maximum of the normalized energy level of thewindow of impulse responses may be represented as 1 (shown as numeral404). The transition from the short training field to the long trainingfield may be identified based on the normalized energy level exceeds apredetermined threshold 406, approximately at point 408. Note that thepredetermined threshold can be represented as a fraction of thenormalized energy level of the window of impulse responses. In someimplementations, the level of threshold may be set to 1/16, ⅛, or ¼ ofthe maximum normalized energy of the channel.

In other implementations, a change of the slope of the normalized energylevel of the impulse responses may be used to identify a transition fromthe short training field to the long training field. In the exampleshown in FIG. 4A, the window of impulse responses prior to the point 412may be relatively flat. After the point 412, a change in slope of theimpulse responses may be observed. If the change of the slope of thenormalized energy level of the impulse responses exceeds a predeterminedthreshold, such as greater than 45 degrees, a transition from the shorttraining field to the long training field may be identified. In someother implementations, the predetermined threshold for the slope of theimpulse response may be set to different values, such as 30 degrees, 50degrees, 60 degrees, or other values.

The first arrival correction (FAC) time 410 may be determined bycomputing a difference between the first arrival time, indicated bypoint 408 in this example, and an expected arrival time, represented bythe origin 412 of graph 402. Note that in the example of FIG. 4A, thetime of transition from STF to LTF is shown as being late with respectto the expected arrival time 412.

FIG. 4B illustrates another exemplary implementation for measuring firstarrival correction time according to aspects of the present disclosure.In this example, the time of transition from STF to LTF is shown asbeing early with respect to the expected arrival time. Similar to theexample shown in FIG. 4A, a station (such as 202 or 204) may beconfigured to monitor a window of impulse responses of a messagereceived. Then, the station may be configured to generate a normalizedenergy level of the window of impulse responses with respect to timeusing the message received, which may be represented by graph 422 asshown in FIG. 4B. The maximum of the normalized energy level of thewindow of impulse responses may be represented as 1 (shown as numeral424). The transition from the short training field to the long trainingfield may be identified based on the normalized energy level exceeds apredetermined threshold 426, approximately at point 428. The firstarrival correction (FAC) time 430 may be determined by computing adifference between the first arrival time, indicated by point 428 inthis example, and an expected arrival time, represented by the origin432 of graph 422.

FIG. 5A illustrates an exemplary flow chart for implementing methods ofimproving quality of positioning according to aspects of the presentdisclosure. In the exemplary implementation shown in FIG. 5A, in block502, the method receives a message at a first station, where the messagecomprises at least a short training field and a long training fieldreceived from a second station. In block 504, the method detects atransition from the short training field to the long training field. Inblock 506, the method determines a first arrival correction time basedat least in part on the transition from the short training field to thelong training field. In block 508, the method assists the second stationto determine a range and/or position of the second station in accordancewith the first arrival correction time.

FIG. 5B illustrates an exemplary implementation for detecting atransition from a short training field to a long training field of FIG.5A according to aspects of the present disclosure. As shown in FIG. 5B,in block 510, the method monitors a window of impulse responses of themessage received. In block 512, the method generates a normalized energylevel of the window of impulse responses with respect to time using themessage received. In block 514, the method identifies the transitionfrom the short training field to the long training field based at leastin part on the normalized energy level exceeds a predeterminedthreshold. According to aspects of the present disclosure, thepredetermined threshold represents a fraction of the normalized energylevel of the window of impulse responses.

FIG. 5C illustrates an exemplary implementation for determining a firstarrival correction time of FIG. 5A according to aspects of the presentdisclosure. In this example, in block 516, the method determines a firstarrival time using the transition from the short training field to thelong training field. In block 518, the method the first arrivalcorrection time according to a difference between the first arrival timeand an expected arrival time.

FIG. 5D illustrates an exemplary implementation for assisting the secondstation to determine a position of FIG. 5A according to aspects of thepresent disclosure. As shown in FIG. 5D, in block 520, the methodtransmits a first message to the second station, where the first messageis used to compute an adjusted time of reception of the first messagefrom the first station using the first arrival correction time and todetermine the range and/or position of the second station based at leastin part on the adjusted time of reception of the first message.

In block 522, the method transmits a second message to the secondstation, where the second message includes an adjusted time stamp fromthe first station, and where the adjusted time stamp from the firststation is used to determine the range and/or position of the secondstation.

In block 524, the adjusted time stamp from the first station comprisesat least one of: a time of reception of acknowledgement from the secondstation plus the first arrival correction time, or the time of receptionof acknowledgement from the second station plus the first arrivalcorrection time and a random noise.

FIG. 6A illustrates another exemplary flow chart for implementingmethods of improving quality of positioning according to aspects of thepresent disclosure. In the exemplary implementation shown in FIG. 6A, inblock 602, the method receives a message at a second station, where themessage comprises at least a short training field and a long trainingfield received from a first station. In block 604, the method detects atransition from the short training field to the long training field. Inblock 606, the method determines a first arrival correction time basedat least in part on the transition from the short training field to thelong training field. In block 608, the method determines a range and/orposition of the second station in accordance with the first arrivalcorrection time.

FIG. 6B illustrates an exemplary implementation for detecting atransition from a short training field to a long training field of FIG.6A according to aspects of the present disclosure. As shown in FIG. 6B,in block 610, the method monitors a window of impulse responses of themessage received. In block 612, the method generates a normalized energylevel of the window of impulse responses with respect to time using themessage received. In block 614, the method identifies the transitionfrom the short training field to the long training field based at leastin part on the normalized energy level exceeds a predeterminedthreshold.

FIG. 6C illustrates an exemplary implementation for determining a firstarrival correction time of FIG. 6A according to aspects of the presentdisclosure. In the exemplary implementation shown in FIG. 6C, in block616, the method determines a first arrival time using the transitionfrom the short training field to the long training field. In block 618,the method determines the first arrival correction time according to adifference between the first arrival time and an expected arrival time.

FIG. 6D illustrates an exemplary implementation for determining a rangeof the second station of FIG. 6A according to aspects of the presentdisclosure. As shown in FIG. 6D, in block 620, the method receives afirst message from the first station; computes an adjusted time ofreception of the first message from the first station using the firstarrival correction time; and determines the range and/or position of thesecond station based at least in part on the adjusted time of receptionof the first message.

In block 622, the method receives a second message from the firststation, where the second message includes an adjusted time stamp fromthe first station; and determines the range and/or position of thesecond station based at least in part on the adjusted time of receptionof the first message and the adjusted time stamp from the first station.

In block 624, the adjusted time stamp from the first station comprisesat least one of: a time of reception of acknowledgement from the secondstation plus the first arrival correction time; or the time of receptionof acknowledgement from the second station plus the first arrivalcorrection time and a random noise.

According to aspects of the present disclosure, in one embodiment, oneor more processors may be configured to receive a message at a secondstation, where the message comprises at least a short training field anda long training field received from a first station, detect a transitionfrom the short training field to the long training field, determine afirst arrival correction time based at least in part on the transitionfrom the short training field to the long training field, and determinea range and/or position of the second station in accordance with thefirst arrival correction time.

To detect the transition from the short training field to the longtraining field, the one or more processors may be configured to monitora window of impulse responses of the message received, generate anormalized energy level of the window of impulse responses with respectto time using the message received, and identify the transition from theshort training field to the long training field based at least in parton the normalized energy level exceeds a predetermined threshold. Thepredetermined threshold may represent a fraction of the normalizedenergy level of the window of impulse responses.

To determine the first arrival correction time, the one or moreprocessors may be configured to determine a first arrival time using thetransition from the short training field to the long training field, anddetermine the first arrival correction time according to a differencebetween the first arrival time and an expected arrival time.

To determine the range and/or position of the second station inaccordance with the first arrival correction time, the one or moreprocessors may be configured to receive a first message from the firststation, compute an adjusted time of reception of the first message fromthe first station using the first arrival correction time, and determinethe range and/or position of the second station based at least in parton the adjusted time of reception of the first message. The one or moreprocessors may be further configured to receive a second message fromthe first station, where the second message includes an adjusted timestamp from the first station, and determine the range and/or position ofthe second station based at least in part on the adjusted time ofreception of the first message and the adjusted time stamp from thefirst station.

Note that the adjusted time stamp from the first station may include atime of reception of acknowledgement from the second station plus thefirst arrival correction time. The adjusted time stamp from the firststation may further include a time of reception of acknowledgement fromthe second station plus the first arrival correction time and a randomnoise.

In another embodiment, a computer program product may includenon-transitory medium storing instructions for execution by one or morecomputer systems. The instructions may further include instructions forreceiving a message at a second station, where the message comprises atleast a short training field and a long training field received from afirst station, instructions for detecting a transition from the shorttraining field to the long training field, instructions for determininga first arrival correction time based at least in part on the transitionfrom the short training field to the long training field, andinstructions for determining a range and/or position of the secondstation in accordance with the first arrival correction time.

In yet another embodiment, a device may include a transceiver configuredto receive a message at the device, where the message comprises at leasta short training field and a long training field received from a firststation, and a control module including control logic and one or moreprocessors. The control logic and the one or more processors may includelogic configured to detect a transition from the short training field tothe long training field, logic configured to determine a first arrivalcorrection time based at least in part on the transition from the shorttraining field to the long training field, and logic configured todetermining a position of the device in accordance with the firstarrival correction time.

In yet another embodiment, an apparatus may include means for receivinga message at the apparatus, where the message comprises at least a shorttraining field and a long training field received from a first station,means for detecting a transition from the short training field to thelong training field, means for determining a first arrival correctiontime based at least in part on the transition from the short trainingfield to the long training field, and means for determining a positionof the apparatus in accordance with the first arrival correction time.

FIG. 7 illustrates an exemplary block diagram of a device according toaspects of the present disclosure. As shown in FIG. 7, mobile device 100(FIG. 1) may comprise one or more features of mobile device 700 shown inFIG. 7. In certain embodiments, mobile device 700 may also comprise awireless transceiver 721 which is capable of transmitting and receivingwireless signals 723 via wireless antenna 722 over a wirelesscommunication network. Wireless transceiver 721 may be connected to bus701 by a wireless transceiver bus interface 720. Wireless transceiverbus interface 720 may, in some embodiments be at least partiallyintegrated with wireless transceiver 721. Some embodiments may includemultiple wireless transceivers 721 and wireless antennas 722 to enabletransmitting and/or receiving signals according to a correspondingmultiple wireless communication standards such as, for example, versionsof IEEE Std. 802.11, CDMA, WCDMA, LTE, UMTS, GSM, AMPS, Zigbee andBluetooth®, etc.

According to aspects of the present disclosure, wireless transceiver 721may comprise a transmitter and a receiver. The transmitter and thereceiver may be implemented to share common circuitry, or may beimplemented as separate circuits. Depending on particular situations ofcommunications between sending STA 202 and receiving station 204 of FIG.2, the wireless transceiver in the sending STA 202 or the receiving STA204 may function as either the transmitter or the receiver, or viceversa. For example, to send a message from sending STA 202 to receivingSTA 204, the wireless transceiver of sending STA 202 acts as atransmitter, and the wireless transceiver of receiving STA 204 acts as areceiver. On the other hand, to send an acknowledgement indicating theabove message has been received the wireless transceiver of receivingSTA 204 acts as a transmitter, and the wireless transceiver of sendingSTA 202 acts as a receiver.

Mobile device 700 may also comprise SPS receiver 755 capable ofreceiving and acquiring SPS signals 759 via SPS antenna 758. SPSreceiver 755 may also process, in whole or in part, acquired SPS signals759 for estimating a location of mobile device 100. In some embodiments,processor(s) 711, memory 740, DSP(s) 712 and/or specialized processors(not shown) may also be utilized to process acquired SPS signals, inwhole or in part, and/or calculate an estimated location of mobiledevice 700, in conjunction with SPS receiver 755. Storage of SPS orother signals for use in performing positioning operations may beperformed in memory 740 or registers (not shown).

Also shown in FIG. 7, mobile device 700 may comprise digital signalprocessor(s) (DSP(s)) 712 connected to the bus 701 by a bus interface710, processor(s) 711 connected to the bus 701 by a bus interface 710and memory 740. Bus interface 710 may be integrated with the DSP(s) 712,processor(s) 711 and memory 740. In various embodiments, functions maybe performed in response execution of one or more machine-readableinstructions stored in memory 740 such as on a computer-readable storagemedium, such as RAM, ROM, FLASH, or disc drive, just to name a fewexample. The one or more instructions may be executable by processor(s)711, specialized processors, or DSP(s) 712. Memory 740 may comprise anon-transitory processor-readable memory and/or a computer-readablememory that stores software code (programming code, instructions, etc.)that are executable by processor(s) 711 and/or DSP(s) 712 to performfunctions described herein. In a particular implementation, wirelesstransceiver 721 may communicate with processor(s) 711 and/or DSP(s) 712through bus 701 to enable mobile device 700 to be configured as awireless STA as discussed above. Processor(s) 711 and/or DSP(s) 712 mayexecute instructions to execute one or more aspects of processes/methodsdiscussed above in connection with FIG. 5A-5D and FIG. 6A-6D.

Also shown in FIG. 7, a user interface 735 may comprise any one ofseveral devices such as, for example, a speaker, microphone, displaydevice, vibration device, keyboard, touch screen, etc. In a particularimplementation, user interface 735 may enable a user to interact withone or more applications hosted on mobile device 700. For example,devices of user interface 735 may store analog or digital signals onmemory 740 to be further processed by DSP(s) 712 or processor 711 inresponse to action from a user. Similarly, applications hosted on mobiledevice 700 may store analog or digital signals on memory 740 to presentan output signal to a user. In another implementation, mobile device 700may optionally include a dedicated audio input/output (I/O) device 770comprising, for example, a dedicated speaker, microphone, digital toanalog circuitry, analog to digital circuitry, amplifiers and/or gaincontrol. In another implementation, mobile device 700 may comprise touchsensors 762 responsive to touching or pressure on a keyboard or touchscreen device.

Mobile device 700 may also comprise a dedicated camera device 764 forcapturing still or moving imagery. Dedicated camera device 764 maycomprise, for example an imaging sensor (e.g., charge coupled device orCMOS imager), lens, analog to digital circuitry, frame buffers, etc. Inone implementation, additional processing, conditioning, encoding orcompression of signals representing captured images may be performed atprocessor 711 or DSP(s) 712. Alternatively, a dedicated video processor768 may perform conditioning, encoding, compression or manipulation ofsignals representing captured images. Additionally, dedicated videoprocessor 768 may decode/decompress stored image data for presentationon a display device (not shown) on mobile device 700.

Mobile device 700 may also comprise sensors 760 coupled to bus 701 whichmay include, for example, inertial sensors and environment sensors.Inertial sensors of sensors 760 may comprise, for example accelerometers(e.g., collectively responding to acceleration of mobile device 700 inthree dimensions), one or more gyroscopes or one or more magnetometers(e.g., to support one or more compass applications). Environment sensorsof mobile device 700 may comprise, for example, temperature sensors,barometric pressure sensors, ambient light sensors, and camera imagers,microphones, just to name few examples. Sensors 760 may generate analogor digital signals that may be stored in memory 740 and processed byDPS(s) or processor 711 in support of one or more applications such as,for example, applications directed to positioning or navigationoperations.

In a particular implementation, mobile device 700 may comprise adedicated modem processor 766 capable of performing baseband processingof signals received and down-converted at wireless transceiver 721 orSPS receiver 755. Similarly, dedicated modem processor 766 may performbaseband processing of signals to be up-converted for transmission bywireless transceiver 721. In alternative implementations, instead ofhaving a dedicated modem processor, baseband processing may be performedby a processor or DSP (e.g., processor 711 or DSP(s) 712).

FIG. 8 illustrates an exemplary block diagram of a computing platformaccording to aspects of the present disclosure. In this example, system800 may include one or more devices configurable to implement techniquesor processes described above, for example, in connection with FIG. 1.System 800 may include, for example, first device 802, second device804, and third device 806, which may be operatively coupled togetherthrough a wireless communications network 808. In an aspect, firstdevice 802 may comprise a server capable of providing positioningassistance data such as, for example, a base station almanac. Second andthird devices 804 and 806 may comprise mobile devices, in an aspect.Also, in an aspect, wireless communications network 808 may comprise oneor more wireless access points, for example.

First device 802, second device 804 and third device 806, as shown inFIG. 8, may be representative of any device, appliance or machine (e.g.,such as local transceiver 108 or servers 140, 150 or 160 as shown inFIG. 1) that may be configurable to exchange data over wirelesscommunications network 808. By way of example but not limitation, any offirst device 802, second device 804, or third device 806 may include:one or more computing devices or platforms, such as, e.g., a desktopcomputer, a laptop computer, a workstation, a server device, or thelike; one or more personal computing or communication devices orappliances, such as, e.g., a personal digital assistant, mobilecommunication device, or the like; a computing system or associatedservice provider capability, such as, e.g., a database or data storageservice provider/system, a network service provider/system, an Internetor intranet service provider/system, a portal or search engine serviceprovider/system, a service access transceiver device capable offacilitating wireless service to a mobile device such as a WLAN accesspoint or femto cell as part of a wireless communication serviceprovider/system; or any combination thereof. Any of the first, second,and third devices 802, 804, and 806, respectively, may comprise one ormore of a base station almanac server, a base station, or a mobiledevice in accordance with the examples described herein.

Similarly, wireless communications network 808 (e.g., in a particular ofimplementation of network 130 shown in FIG. 1), may be representative ofone or more communication links, processes, or resources configurable tosupport the exchange of data between at least two of first device 802,second device 804, and third device 806. By way of example but notlimitation, communications network 808 may include wireless or wiredcommunication links, telephone or telecommunications systems, data busesor channels, optical fibers, terrestrial or space vehicle resources,local area networks, wide area networks, intranets, the Internet,routers or switches, and the like, or any combination thereof. Asillustrated, for example, by the dashed lined box illustrated as beingpartially obscured of third device 806, there may be additional likedevices operatively coupled to wireless communications network 808.

It is recognized that all or part of the various devices and networksshown in system 800, and the processes and methods as further describedherein, may be implemented using or otherwise including hardware,firmware, software, or any combination thereof. Thus, by way of examplebut not limitation, second device 804 may include at least oneprocessing unit 820 that is operatively coupled to a memory 822 througha bus 828.

Processing unit 820 is representative of one or more circuitsconfigurable to perform at least a portion of a data computing procedureor process. By way of example but not limitation, processing unit 820may include one or more processors, controllers, microprocessors,microcontrollers, application specific integrated circuits, digitalsignal processors, programmable logic devices, field programmable gatearrays, and the like, or any combination thereof. Wireless transceiver842 may communicate with processing unit 820 through bus 828 to enablesecond device 804 to be configured as a wireless STA as discussed above.Processing unit 820 may execute instructions to execute one or moreaspects of processes/methods discussed above in connection with FIG.5A-5D and FIG. 6A-6D.

Memory 822 is representative of any data storage mechanism. Memory 822may include, for example, a primary memory 824 or a secondary memory826. Primary memory 824 may include, for example, a random accessmemory, read only memory, etc. While illustrated in this example asbeing separate from processing unit 820, it should be understood thatall or part of primary memory 824 may be provided within or otherwiseco-located/coupled with processing unit 820.

Secondary memory 826 may include, for example, the same or similar typeof memory as primary memory or one or more data storage devices orsystems, such as, for example, a disk drive, an optical disc drive, atape drive, a solid state memory drive, etc. In certain implementations,secondary memory 826 may be operatively receptive of, or otherwiseconfigurable to couple to, a computer-readable medium 840.Computer-readable medium 840 may include, for example, anynon-transitory medium that can carry or make accessible data, code orinstructions for one or more of the devices in system 800.Computer-readable medium 840 may also be referred to as a storagemedium.

Second device 804 may include, for example, a communication interface1030 that provides for or otherwise supports the operative coupling ofsecond device 804 to at least wireless communications network 808. Byway of example but not limitation, communication interface 830 mayinclude a network interface device or card, a modem, a router, a switch,a transceiver, and the like.

Second device 804 may include, for example, an input/output device 832.Input/output device 832 is representative of one or more devices orfeatures that may be configurable to accept or otherwise introduce humanor machine inputs, or one or more devices or features that may beconfigurable to deliver or otherwise provide for human or machineoutputs. By way of example but not limitation, input/output device 832may include an operatively configured display, speaker, keyboard, mouse,trackball, touch screen, data port, etc.

Note that the paragraphs herein, FIG. 1, FIG. 5A-5D, FIG. 7, FIG. 8 andtheir corresponding descriptions provide means for receiving a messageat the apparatus, means for detecting a transition from the shorttraining field to the long training field, means for determining a firstarrival correction time based at least in part on the transition fromthe short training field to the long training field, means for assistingthe second station to determine a range of the second station inaccordance with the first arrival correction time, means for monitoringa window of impulse responses of the message received, means forgenerating a normalized energy level of the window of impulse responseswith respect to time using the message received, means for identifyingthe transition from the short training field to the long training fieldbased at least in part on the normalized energy level exceeds apredetermined threshold, means for determining a first arrival timeusing the transition from the short training field to the long trainingfield, means for determining the first arrival correction time accordingto a difference between the first arrival time and an expected arrivaltime, means for transmitting a first message to the second station, andmeans for transmitting a second message to the second station.

Note that the paragraphs herein, FIG. 1, FIG. 6A-6D, FIG. 7, FIG. 8 andtheir corresponding descriptions provide means for receiving a messageat the apparatus, means for detecting a transition from the shorttraining field to the long training field, means for determining a firstarrival correction time based at least in part on the transition fromthe short training field to the long training field, means fordetermining a position of the apparatus in accordance with the firstarrival correction time, means for monitoring a window of impulseresponses of the message received, means for generating a normalizedenergy level of the window of impulse responses with respect to timeusing the message received, means for identifying the transition fromthe short training field to the long training field based at least inpart on the normalized energy level exceeds a predetermined threshold,means for determining a first arrival time using the transition from theshort training field to the long training field, means for determiningthe first arrival correction time according to a difference between thefirst arrival time and an expected arrival time, means for receiving afirst message from the first station, means for computing an adjustedtime of reception of the first message from the first station using thefirst arrival correction time, means for determining the position of theapparatus based at least in part on the adjusted time of reception ofthe first message, means for receiving a second message from the firststation, and means for determining the position of the apparatus basedat least in part on the adjusted time of reception of the first messageand the adjusted time stamp from the first station.

The methodologies described herein may be implemented by various meansdepending upon applications according to particular examples. Forexample, such methodologies may be implemented in hardware, firmware,software, or combinations thereof. In a hardware implementation, forexample, a processing unit may be implemented within one or moreapplication specific integrated circuits (“ASICs”), digital signalprocessors (“DSPs”), digital signal processing devices (“DSPDs”),programmable logic devices (“PLDs”), field programmable gate arrays(“FPGAs”), processors, controllers, micro-controllers, microprocessors,electronic devices, other devices units designed to perform thefunctions described herein, or combinations thereof.

Some portions of the detailed description included herein are presentedin terms of algorithms or symbolic representations of operations onbinary digital signals stored within a memory of a specific apparatus orspecial purpose computing device or platform. In the context of thisparticular specification, the term specific apparatus or the likeincludes a general purpose computer once it is programmed to performparticular operations pursuant to instructions from program software.Algorithmic descriptions or symbolic representations are examples oftechniques used by those of ordinary skill in the signal processing orrelated arts to convey the substance of their work to others skilled inthe art. An algorithm is here, and generally, is considered to be aself-consistent sequence of operations or similar signal processingleading to a desired result. In this context, operations or processinginvolve physical manipulation of physical quantities. Typically,although not necessarily, such quantities may take the form ofelectrical or magnetic signals capable of being stored, transferred,combined, compared or otherwise manipulated. It has proven convenient attimes, principally for reasons of common usage, to refer to such signalsas bits, data, values, elements, symbols, characters, terms, numbers,numerals, or the like. It should be understood, however, that all ofthese or similar terms are to be associated with appropriate physicalquantities and are merely convenient labels. Unless specifically statedotherwise, as apparent from the discussion herein, it is appreciatedthat throughout this specification discussions utilizing terms such as“processing,” “computing,” “calculating,” “determining” or the likerefer to actions or processes of a specific apparatus, such as a specialpurpose computer, special purpose computing apparatus or a similarspecial purpose electronic computing device. In the context of thisspecification, therefore, a special purpose computer or a similarspecial purpose electronic computing device is capable of manipulatingor transforming signals, typically represented as physical electronic ormagnetic quantities within memories, registers, or other informationstorage devices, transmission devices, or display devices of the specialpurpose computer or similar special purpose electronic computing device.

Wireless communication techniques described herein may be in connectionwith various wireless communications networks such as a wireless widearea network (“WWAN”), a wireless local area network (“WLAN”), awireless personal area network (WPAN), and so on. The term “network” and“system” may be used interchangeably herein. A WWAN may be a CodeDivision Multiple Access (“CDMA”) network, a Time Division MultipleAccess (“TDMA”) network, a Frequency Division Multiple Access (“FDMA”)network, an Orthogonal Frequency Division Multiple Access (“OFDMA”)network, a Single-Carrier Frequency Division Multiple Access (“SC-FDMA”)network, or any combination of the above networks, and so on. A CDMAnetwork may implement one or more radio access technologies (“RATs”)such as cdma2000, Wideband-CDMA (“W-CDMA”), to name just a few radiotechnologies. Here, cdma2000 may include technologies implementedaccording to IS-95, IS-2000, and IS-856 standards. A TDMA network mayimplement Global System for Mobile Communications (“GSM”), DigitalAdvanced Mobile Phone System (“D-AMPS”), or some other RAT. GSM andW-CDMA are described in documents from a consortium named “3rdGeneration Partnership Project” (“3GPP”). Cdma2000 is described indocuments from a consortium named “3rd Generation Partnership Project 2”(“3GPP2”). 3GPP and 3GPP2 documents are publicly available. 4G Long TermEvolution (“LTE”) communications networks may also be implemented inaccordance with claimed subject matter, in an aspect. A WLAN maycomprise an IEEE 802.11x network, and a WPAN may comprise a Bluetooth®network, an IEEE 802.15x, for example. Wireless communicationimplementations described herein may also be used in connection with anycombination of WWAN, WLAN or WPAN.

In another aspect, as previously mentioned, a wireless transmitter oraccess point may comprise a femtocell, utilized to extend cellulartelephone service into a business or home. In such an implementation,one or more mobile devices may communicate with a femtocell via a codedivision multiple access (“CDMA”) cellular communication protocol, forexample, and the femtocell may provide the mobile device access to alarger cellular telecommunication network by way of another broadbandnetwork such as the Internet.

Techniques described herein may be used with an SPS that includes anyone of several GNSS and/or combinations of GNSS. Furthermore, suchtechniques may be used with positioning systems that utilize terrestrialtransmitters acting as “pseudolites”, or a combination of SVs and suchterrestrial transmitters. Terrestrial transmitters may, for example,include ground-based transmitters that broadcast a PN code or otherranging code (e.g., similar to a GPS or CDMA cellular signal). Such atransmitter may be assigned a unique PN code so as to permitidentification by a remote receiver. Terrestrial transmitters may beuseful, for example, to augment an SPS in situations where SPS signalsfrom an orbiting SV might be unavailable, such as in tunnels, mines,buildings, urban canyons or other enclosed areas. Another implementationof pseudolites is known as radio-beacons. The term “SV”, as used herein,is intended to include terrestrial transmitters acting as pseudolites,equivalents of pseudolites, and possibly others. The terms “SPS signals”and/or “SV signals”, as used herein, is intended to include SPS-likesignals from terrestrial transmitters, including terrestrialtransmitters acting as pseudolites or equivalents of pseudolites.

The terms, “and,” and “or” as used herein may include a variety ofmeanings that will depend at least in part upon the context in which itis used. Typically, “or” if used to associate a list, such as A, B or C,is intended to mean A, B, and C, here used in the inclusive sense, aswell as A, B or C, here used in the exclusive sense. Referencethroughout this specification to “one example” or “an example” meansthat a particular feature, structure, or characteristic described inconnection with the example is included in at least one example ofclaimed subject matter. Thus, the appearances of the phrase “in oneexample” or “an example” in various places throughout this specificationare not necessarily all referring to the same example. Furthermore, theparticular features, structures, or characteristics may be combined inone or more examples. Examples described herein may include machines,devices, engines, or apparatuses that operate using digital signals.Such signals may comprise electronic signals, optical signals,electromagnetic signals, or any form of energy that provides informationbetween locations.

While there has been illustrated and described what are presentlyconsidered to be example features, it will be understood by thoseskilled in the art that various other modifications may be made, andequivalents may be substituted, without departing from claimed subjectmatter. Additionally, many modifications may be made to adapt aparticular situation to the teachings of claimed subject matter withoutdeparting from the central concept described herein. Therefore, it isintended that claimed subject matter not be limited to the particularexamples disclosed, but that such claimed subject matter may alsoinclude all aspects falling within the scope of the appended claims, andequivalents thereof.

What is claimed is:
 1. A method of determining a range between twostations, comprising: receiving a message at a first station, whereinthe message comprises at least a short training field and a longtraining field received from a second station; detecting a transitionfrom the short training field to the long training field, comprisingmonitoring a window of impulse responses of the message received,generating a normalized energy level of the window of impulse responseswith respect to time using the message received, and identifying thetransition from the short training field to the long training fieldbased, at least in part, on: a slope of the normalized energy levelexceeding a predetermined threshold of the slope of the normalizedenergy level; determining a first arrival correction time based at leastin part on the transition from the short training field to the longtraining field; and assisting the second station to determine a range ofthe second station in accordance with the first arrival correction time.2. The method of claim 1, wherein the predetermined threshold representsa fraction of the normalized energy level of the window of impulseresponses.
 3. The method of claim 1, wherein the determining the firstarrival correction time comprises: determining a first arrival timeusing the transition from the short training field to the long trainingfield; and determining the first arrival correction time according to adifference between the first arrival time and an expected arrival time.4. The method of claim 1, wherein the assisting the second station todetermine the range of the second station in accordance with the firstarrival correction time comprises: transmitting a first message to thesecond station, wherein the first message is used to compute an adjustedtime of reception of the first message from the first station using thefirst arrival correction time and to determine the range of the secondstation based at least in part on the adjusted time of reception of thefirst message.
 5. The method of claim 4, wherein the assisting thesecond station to determine the range of the second station inaccordance with the first arrival correction time further comprises:transmitting a second message to the second station, wherein the secondmessage includes an adjusted time stamp from the first station, andwherein the adjusted time stamp from the first station is used todetermine the range of the second station.
 6. The method of claim 5,wherein the adjusted time stamp from the first station comprises: a timeof reception of acknowledgement from the second station plus the firstarrival correction time.
 7. The method of claim 5, wherein the adjustedtime stamp from the first station further comprises: a time of receptionof acknowledgement from the second station plus the first arrivalcorrection time and a random noise.
 8. A computer program productcomprising a non-transitory medium storing instructions for execution byone or more computer systems, the instructions comprising: instructionsfor receiving a message at a first station, wherein the messagecomprises at least a short training field and a long training fieldreceived from a second station; instructions for detecting a transitionfrom the short training field to the long training field, comprisinginstructions for monitoring a window of impulse responses of the messagereceived, instructions for generating a normalized energy level of thewindow of impulse responses with respect to time using the messagereceived, and instructions for identifying the transition from the shorttraining field to the long training field based, at least in part, on: aslope of the normalized energy level exceeding a predetermined thresholdof the slope of the normalized energy level; instructions fordetermining a first arrival correction time based at least in part onthe transition from the short training field to the long training field;and instructions for assisting the second station to determine a rangeof the second station in accordance with the first arrival correctiontime.
 9. The computer program product of claim 8, wherein thepredetermined threshold represents a fraction of the normalized energylevel of the window of impulse responses.
 10. The computer programproduct of claim 8, wherein the instructions for determining the firstarrival correction time comprises: instructions for determining a firstarrival time using the transition from the short training field to thelong training field; and instructions for determining the first arrivalcorrection time according to a difference between the first arrival timeand an expected arrival time.
 11. The computer program product of claim8, wherein the instructions for assisting the second station todetermine the range of the second station in accordance with the firstarrival correction time comprises: instructions for transmitting a firstmessage to the second station, wherein the first message is used tocompute an adjusted time of reception of the first message from thefirst station using the first arrival correction time and to determinethe range of the second station based at least in part on the adjustedtime of reception of the first message.
 12. The computer program productof claim 11, wherein the instructions for assisting the second stationto determine the range of the second station in accordance with thefirst arrival correction time further comprises: instructions fortransmitting a second message to the second station, wherein the secondmessage includes an adjusted time stamp from the first station, andwherein the adjusted time stamp from the first station is used todetermine the range of the second station.
 13. The computer programproduct of claim 12, wherein the adjusted time stamp from the firststation comprises: a time of reception of acknowledgement from thesecond station plus the first arrival correction time.
 14. The computerprogram product of claim 12, wherein the adjusted time stamp from thefirst station further comprises: a time of reception of acknowledgementfrom the second station plus the first arrival correction time and arandom noise.
 15. A device, comprising: a transceiver configured toreceive a message at the device, wherein the message comprises at leasta short training field and a long training field received from a secondstation; one or more processors or digital signal processors orcombination thereof configured to detect a transition from the shorttraining field to the long training field, comprising monitor a windowof impulse responses of the message received, generate a normalizedenergy level of the window of impulse responses with respect to timeusing the message received, and identify the transition from the shorttraining field to the long training field based, at least in part, on: aslope of the normalized energy level exceeding a predetermined thresholdof the slope of the normalized energy level; determine a first arrivalcorrection time based at least in part on the transition from the shorttraining field to the long training field; and assist the second stationto determine a range of the second station in accordance with the firstarrival correction time.
 16. The device of claim 15, wherein the one ormore processors or digital signal processors or combination thereofconfigured to determine the first arrival correction time are furtherconfigured to: determine a first arrival time using the transition fromthe short training field to the long training field; and determine thefirst arrival correction time according to a difference between thefirst arrival time and an expected arrival time.
 17. The device of claim15, wherein the one or more processors or digital signal processors orcombination thereof configured to assist the second station to determinethe range of the second station in accordance with the first arrivalcorrection time are further configured to: transmit a first message tothe second station, wherein the first message is used to compute anadjusted time of reception of the first message from the device usingthe first arrival correction time and to determine the range of thesecond station based at least in part on the adjusted time of receptionof the first message.
 18. The device of claim 17, wherein the one ormore processors or digital signal processors or combination thereofconfigured to assist the second station to determine the range of thesecond station in accordance with the first arrival correction timefurther are further configured to: transmit a second message to thesecond station, wherein the second message includes an adjusted timestamp from the device, and wherein the adjusted time stamp from thedevice is used to determine the range of the second station.
 19. Thedevice of claim 18, wherein the adjusted time stamp from the devicecomprises: a time of reception of acknowledgement from the secondstation plus the first arrival correction time.
 20. The device of claim18, wherein the adjusted time stamp from the device further comprises: atime of reception of acknowledgement from the second station plus thefirst arrival correction time and a random noise.
 21. An apparatus,comprising: means for receiving a message at the apparatus, wherein themessage comprises at least a short training field and a long trainingfield received from a second station; means for detecting a transitionfrom the short training field to the long training field, comprisingmeans for monitoring a window of impulse responses of the messagereceived, means for generating a normalized energy level of the windowof impulse responses with respect to time using the message received,and means for identifying the transition from the short training fieldto the long training field based, at least in part, on: a slope of thenormalized energy level exceeding a predetermined threshold of the slopeof the normalized energy level; means for determining a first arrivalcorrection time based at least in part on the transition from the shorttraining field to the long training field; and means for assisting thesecond station to determine a range of the second station in accordancewith the first arrival correction time.
 22. The apparatus of claim 21,wherein the means for determining the first arrival correction timecomprises: means for determining a first arrival time using thetransition from the short training field to the long training field; andmeans for determining the first arrival correction time according to adifference between the first arrival time and an expected arrival time.23. The apparatus of claim 21, wherein the means for assisting thesecond station to determine the range of the second station inaccordance with the first arrival correction time comprises: means fortransmitting a first message to the second station, wherein the firstmessage is used to compute an adjusted time of reception of the firstmessage from the apparatus using the first arrival correction time andto determine the range of the second station based at least in part onthe adjusted time of reception of the first message.
 24. The apparatusof claim 23, wherein the means for assisting the second station todetermine the range of the second station in accordance with the firstarrival correction time further comprises: means for transmitting asecond message to the second station, wherein the second messageincludes an adjusted time stamp from the apparatus, and wherein theadjusted time stamp from the apparatus is used to determine the range ofthe second station.
 25. The apparatus of claim 24, wherein the adjustedtime stamp from the apparatus comprises: a time of reception ofacknowledgement from the second station plus the first arrivalcorrection time.
 26. The apparatus of claim 24, wherein the adjustedtime stamp from the apparatus further comprises: a time of reception ofacknowledgement from the second station plus the first arrivalcorrection time and a random noise.